(1) Field of the Invention
The present invention relates to a method for forming an array of optical fibers for optical communication, and more particularly to a method for forming an array of optical fibers having a tip capable of being efficiently optically coupled with an optical element.
(2) Description of the Related Art
A conventional optical fiber intended to be capable of being efficiently coupled with an optical element has a spherical tip but the spherical tip is limited to a core part of the tip only. In such a conventional optical fiber, the tip of the core exposed by etching is heated and is made spherical. This is advantageous especially when arrays of optical fibers to be optically coupled respectively with a plurality of optical elements are manufactured since a number of the optical fibers arranged in array form can be subjected to simultaneous heat treatment for making them spherical with a low manufacturing cost. This method is disclosed in Japanese Patent Application No. Hei 4-35, published as Patent Application Kokai Publication No. Hei 5-224098 (Optical coupling circuit and manufacture thereof).
Also, there is a conventional optical fiber in which, in an opposite arrangement to the above explained conventional optical fiber, the core at the tip has a recess (jack). A protuberance (plug) formed in an optical coupling lens is inserted into the recess (jack). Similarly as in the first mentioned conventional example, the recess is made by etching the core of the fiber. This method is disclosed in a paper entitled "Put-in Micro-connecters for Alignment-Free Coupling of Optical Fiber Arrays" by A. Sasaki et al, presented at Fourth Optoelectronics Conference (OEC'92) Technical Digest, pp. 136-137, July 1992.
In the optical fiber in general, a resin-made coating material is used to cover and protect a fiber made of glass. However, in the process of etching an end face of the fiber, the etching solution tends to enter into the coating material of the fiber. This causes the coating material to dissolve, makes it difficult to protect the fiber and lowers the reliability of the optical fiber. Especially, in the case of an array of optical fibers which includes a plurality of constituent optical fibers covered by the protective material, the dissolution of the coating material develops, resulting in difficulties in protecting the fibers inside the coating material, and in the occurrence of irregular orientations of tip ends of the fibers, uneven lengths of the projected portions of ends of the fibers and uneven positions of tip ends of the fiber. The problem which results therefrom is that the optical coupling efficiency between the optical elements and respective fibers becomes unsecured gives rise to difficulties in obtaining the desired optical coupling characteristics.
Also, generally, the optical fiber is placed along a groove in a V-shape in cross section and is fixed by being sandwiched between the groove and a flat substrate. However, in the process of etching in order to make the core tip spherical, not only the end face of the fiber but also an adjacent side portion is also etched, so that the fiber tip diameter becomes reduced. This requires that the depth of the V-shaped groove which holds the fiber be changed according to each set of the conditions for the fiber etching. Thus, the problem is that the fixing jig for this purpose becomes costly, thus increasing the manufacturing cost for optical fibers.